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CEO Dennis Muilenberg tweeted a video where he said the test flight was carried out on Tuesday, adding that test pilots have completed 120 flights totaling more than 203 hours of airtime with the software fix for the Maneuvering Characteristics Augmentation System (MCAS).

Investigators have zeroed in on the system as a factor behind the Lion Air and Ethiopian Airlines crashes in October and in March respectively, killing nearly 350 people in total.

In both cases, the planes nose-dived shortly after takeoff, signaling a problem in a system that was deployed to correct for an aerodynamic issue that tended to cause the plane's nose to pitch up.

"More than 85 percent of the 50-plus MAX operators around the globe also have had the opportunity to see the update in action during simulator sessions," added Muilenberg.

All 737 MAX aircraft have been banned from the world's skies since days after the Ethiopian Airlines crash on March 10.

The Federal Aviation Administration on Tuesday said a portion of the proposed modifications were "operationally suitable" but said it would not rush towards approval.